Whale acrobatics inspire a faster helicopter

The way the humpback whale, Megaptera novaeangliae, manages to perform underwater acrobatics and turn on a dime - despite having pendulous, outsize pectoral fins - has inspired aviation engineers in Göttingen, Germany to make a faster, quieter helicopter rotor blade.

A helicopter has a rotor whose aerofoil-shaped blades provides lift, directional control and forward thrust. As the rotor spins, the advancing blade - which is moving in the same direction as the craft - is travelling faster than the retreating blade on the opposite side. These different speeds make for turbulence, vibration and instability - especially during fast flight and whilst turning, when the retreating blade is more likely to lose lift and "stall". As a result, helicopter engineers spend a lot of time trying to minimise this effect.

Noting the humpback's agility in water, Kai Richter and colleagues at the German Aerospace Centre (DLR) wondered if something analagous to the bumps on its pectoral fins - known to provide lift underwater and boost the creature's buoyancy - could help them improve chopper design. Scaling those bumps down relative to a rotor's width, they made 6-millimetre-diameter rubber grommets and fastened 186 of them to the leading edges of the rotors on a test helicopter (see picture, above).

It did indeed significantly delay stalling and the difference has already been noticed by test pilots, Kai says, providing a smoother ride. They have been encouraged enough by their results to file patents on the idea, and they now plan further tests. If their whale mimicry pans out, it won't involve clunky rubber grommets: the bumps would be milled into blades during manufacturing.

I humbly submit that acrobatics must be an activity performed at height, rather than underwater.

Jason
on February 1, 2012 2:38 AM

Explain to me how the advancing blade is moving faster than the retreating blade? My intuition tells me that the advancing blade is pushing against the oncoming air and therefore slowed down slightly while the retreating blade is flowing with the air and would be able to rotate slightly faster. Then again, I thought the rotors were fixed and would be unable to move at unequal relative velocities. I really don't know.

methinks
on February 1, 2012 10:13 AM

The blades are fixed - the advancing blade is moving faster through the air. As lift is only provided by moving through the air, if the retreating blade moves more slowly through it then it provides less lift, hence the possibility of "stalling".

Tom Potts
on February 1, 2012 10:34 AM

So you can patent natural process' now?
I'm going for 'walking'

Josh
on February 1, 2012 10:50 AM

I assume if a helicopters blades are rotating clockwise whilst trying turn right the speed through the air may be the same but the relative speed to the chopper would be different. Same if a chopper is moving forward the blades moving towards the front of the chopper would be slower relatively.

Nick
on February 1, 2012 12:20 PM

They mean the air speed of each blade. So while the helicopter travels forward the blade spinning forward will give more lift than the blade spinning backward as the airspeed over the blades will be different.

neugjl
on February 1, 2012 12:27 PM

Hi Jason
The speed is related to the wind.

Joe
on February 1, 2012 12:56 PM

Ilane, spot on. 'Acrobat' derives from the word 'Acropolis', the highest place in ancient Greece.

Jason, they're talking about airspeed, silly. If you push against the wind (rotor blades are not slowed down by this) you necessarily have a higher airspeed than if you travel with the wind. A leaf in the wind, for example, has negligible airspeed, even in a hurricane.

Enrico
on February 1, 2012 1:39 PM

The fluid dynamics will depend on the force of the air against each rotor blade. Strictly speaking the rotational velocity of each blade will add/subtract to/from the translational velocity of the craft to yeild varying component velocities for each blade (advancing travels faster)
I don't believe that the team should be allowed a patent for this technology as it is already in use for windpower systems and industrial fans. Whalepower has already covered the potential application to flight systems and thus DLR does not have an inventive step.
The world is too patent hungry and the current patent system now slows human technological progress rather than expediates it. Should we really be able to patent technology borrowed from nature anyway???

Jim
on February 1, 2012 1:52 PM

@Jason the speed is different for each blade relative to oncoming air not relative to each other - as you rightly say they are fixed so rotate at the same speed. The advancing blade is pushing in to the air faster and so gets more lift. Whereas the retreating blade could potentially retreat at the same speed as the oncoming air and so stall. How the whales worked this out i dont know.

robert
on February 2, 2012 5:49 AM

it's quite easy to explain why the rotors travel at different speeds. imagine yourself in a bus is traveling 55 miles an hour. If you're walking from the back to the front at 2 miles an hour, you are actually at 57 mph. Subsequently, walking from front to back at 2 miles an hour 53 mph,it's simple physics,

Cabeza de Vaca
on February 2, 2012 3:31 PM

......post script.....

I wrote that the retreating blade can not stall, that is not accurate. it can but the compressibility limit is reached before that occurs. the limiting factor in forward flight is the relative speed of the advancing blade ...

Rotorhead1871
on February 6, 2012 4:22 AM

Ilane on January 31, 2012 10:48 PM

I humbly submit that acrobatics must be an activity performed at height, rather than underwater.

------those would be aerobatics.......

Brian
on February 7, 2012 7:40 PM

they are several years late with this idea as it is allready patented by Whale Power and tested on wind turbine blades.